The present invention relates to catalyst components for the polymerization of olefins, to the catalysts obtained therefrom and to the use of said catalysts in the polymerization of olefins CH2xe2x95x90CHR in which R is hydrogen or a hydrocarbyl radical with 1-12 carbon atoms. In particular the present invention relates to catalyst components, suitable for the stereospecific polymerization of olefins, comprising Ti, Mg, halogen and an electron donor compound selected from heteroatom containing esters of malonic acids (heteroatom containing malonates). Said catalyst components when used in the polymerization of olefins, and in particular of propylene, are capable to give polymers in high yields and with high isotactic index expressed in terms of high xylene insolubility.
The use of some esters of malonic acid as internal electron donors in catalysts for the polymerization of propylene is already known in the art.
In EP-A-45977 is disclosed the use of an ester of malonic acid (diethyl 2,2-diisobutylmalonate) as internal donor of a catalyst for the polymerization of olefins. EP-A-86473 discloses a catalyst for the polymerization of olefins comprising (a) an Al-alkyl compound, (b) an electron donor compound having certain reactivity features towards MgCl2 and (c) a solid catalyst component comprising, supported on MgCl2, a Ti halide and an electron donor selected from many classes of ester compounds including malonates. None of the above-cited applications discloses malonates containing heteroatoms. The same applies to EP-A-86644 that discloses the use of diethyl 2-n-butyl malonate and diethyl 2-isopropylmalonate as internal donors in Mg-supported catalysts for the polymerization of propylene.
It is apparent from the analysis of the polymerization results reported in the above-mentioned applications that a common drawback experienced in the use of the mentioned malonates was represented by a still unsatisfactory polymerization yield and/or a not suitable isotactic index of the final polymer. This is confirmed also by the disclosure of JP-08157521. This application relates to a process for preparing a solid catalyst component for polymerization of olefins which is characterized by contacting a solid catalyst component produced by the reaction among a magnesium compound, a titanium compound and an halogen compound. With one or more electron donating compounds represented by the general formula: 
wherein Rc and Rd are, the same or different, a straight-chain or branched-chain hydrocarbon group having 1-10 carbon atoms, and Ra and Rb are the same or different, a saturated or cyclic saturated hydrocarbon group containing one or more secondary or tertiary carbons and having 3-20 carbon atoms. Although an improvement in terms of yields and isotactic index over the previously cited documents is obtained, the results are still not satisfactory for an economical use of the catalyst components disclosed therein.
It has now surprisingly been found that the polymerization yields and the isotactic index of the polymer can be improved by using catalyst components comprising heteroatom containing malonates as internal donors.
It is therefore an object of the present invention to provide a solid catalyst component for the polymerization of olefins CH2xe2x95x90CHR in which R is hydrogen or a hydrocarbon radical with 1-12 carbon atoms, comprising Mg, Ti, halogen and an heteroatom containing malonate.
The term heteroatom means any atom, different from C and H, in addition to the oxygen atoms deriving from the malonic acid.
In particular, the electron donor compounds can be selected from esters of malonic acids of formula (I): 
wherein R1 and R2 equal to or different from each other, are H or a C1-C20 linear or branched alkyl, alkenyl, cycloalkyl, aryl, arylalkyl or alkylaryl group and said R1 and R2 can also be joined to form a cyclic group; R3 and R4 are independently selected from C1-C20 linear or branched alkyl, alkenyl, cycloalkyl, aryl, arylalkyl or alkylaryl group and R3 and R4 can also be joined to form a cyclic group; with the proviso that at least one of the R1 to R4 groups contains at least one heteroatom selected from the group consisting of halogens, N, O, Si, Ge, P, and S.
The heteroatoms, are preferably selected from the group consisting of F, Cl, Br, and Si, and, in a preferred embodiment, they are contained in the R1 or R2 groups.
Preferably, R3 and R4 are primary alkyl, arylalkyl or alkylaryl groups having from 2 to 8 carbon atoms which may contain heteroatoms. More preferably, they are primary branched alkyl groups optionally containing heteroatoms. Examples of suitable R3 and R4 groups not containing heteroatoms are methyl, ethyl, n-propyl, n-butyl, isobutyl, neopentyl, 2-ethylhexyl. Examples of suitable R3 and R4 groups containing heteroatoms are 2-chloroethyl, 1-trifluoromethylethyl, 2-trifluoromethylpropyl 2-trimethylsilylethyl, 2-bromoethyl, 2-trifluoromethylpropyl, 4-chlorobenzyl, 2-fluoroethyl, 3-trimethylsilylallyl.
R2 is preferably, and particularly when R1 is H, a linear or branched C3-C20 alkyl, cycloalkyl, arylalkyl group; more preferably R2 is a C3-C20 secondary alkyl, cycloalkyl, or arylalkyl. Particularly preferred are also compounds of formula (I) in which R1 is H and R2 is a C5-C20 primary linear or branched alkyl, a C5-C20 cycloalkyl, a C7-C20 arylalkyl or alkylaryl group. Preferably R2 contains at least one heteroatom. Specific examples of suitable monosubstituted malonate compounds are diethyl 2-(1-trifluoromethylethyl) malonate, diethyl 2-(1-trifluoromethylethylidene)malonate, bis(2-chloroethyl) 2-isopropylmalonate, diethyl 2-(trimethylsilylmethyl)malonate, diethyl 2-p-chlorobenzylmalonate, diethyl 2-piperidyl malonate, diethyl 2-(2-ethylpiperidyl)malonate, diethyl 2-(1-trifluoromethyl-1-methylethyl)malonate, diethyl 2-xcex1-phenyl-p-(trifluoromethyl)benzyl malonate, bis(2-fluoroethyl) 2-isopropylmalonate, bis(2-fluoroethyl) 2-ethylmalonate.
Among disubstituted malonates preferred compounds are those in which at least one of R1 and R2 is a primary C3-C20 alkyl, cycloalkyl, arylalkyl group.
Specific examples of suitable disubstituted malonate compounds are: diethyl-2(1-trifluoromethylethyl)-2-benzylmalonate, diethyl 2-(1-trifluoromethylethyl)-2-methylmalonate, diethyl 2-methyltrimethylsilyl-2-methylmalonate, diethyl 2-p-chlorobenzyl-2-isopropylmalonate, diethyl 2-piperidyl-2-methylmalonate, diethyl 2-(1-trifluoromethyl-1-methylethyl)-2-methylmalonate, bis(2-trimethylsilylethyl) 2-isopropyl-2-isobutylmalonate bis(p-chlorobenzyl) 2-cyclohexyl-2-methylmalonate.
It has been surprisingly found that catalyst components in which the internal donor is a heteroatom containing malonate perform better, in term of yields and isotactic index, than catalyst components comprising analogous malonates not containing heteroatoms.
As explained above, catalyst components according to the invention comprise, in addition to the above electron donor, Ti, Mg and halogen. In particular, the catalyst component comprises a titanium compound, having at least a Ti-halogen bond and the above mentioned electron donor compound supported on a Mg halide. The magnesium halide is preferably MgCl2 in active form which is widely known from the patent literature as a support for Ziegler-Natta catalysts. Patents U.S. Pat. Nos. 4,298,718 and 4,495,388 were the first to describe the use of these compounds in Ziegler-Natta catalysis. It is known from these patents that the magnesium dihalides in active form used as support or co-support in components of catalysts for the polymerization of olefins are characterized by X-ray spectra in which the most intense diffraction line that appears in the spectrum of the non-active halide is diminished in intense and is replaced by a halo whose maximum intensity is displaced towards lower angles relative to that of the more intense line.
The preferred titanium compounds used in the catalyst component of the present invention are TiCl4 and TiCl3; furthermore, also Ti-haloalcoholates of formula Ti(OR)nxe2x88x92yXy, where n is the valence of titanium and y is a number between 1 and n, can be used.
The preparation of the solid catalyst component can be carried out according to several methods.
According to one of these methods, the magnesium dichloride in an anhydrous state and the heteroatom containing malonate are milled together under conditions in which activation of the magnesium dichloride occurs. The so obtained product can be treated one or more times with an excess of TiCl4 at a temperature between 80 and 135xc2x0 C. This treatment is followed by washings with hydrocarbon solvents until chloride ions disappear. According to a further method, the product obtained by co-milling the magnesium chloride in an anhydrous state, the titanium compound and the heteroatom containing malonate is treated with halogenated hydrocarbons such as 1,2-dichloroethane, chlorobenzene, dichloromethane etc. The treatment is carried out for a time between 1 and 4 hours and at temperature of from 40xc2x0 C. to the boiling point of the halogenated hydrocarbon. The product obtained is then generally washed with inert hydrocarbon solvents such as hexane.
According to another method, magnesium dichloride is preactivated according to well known methods and then treated with an excess of TiCl4 at a temperature of about 80 to 135xc2x0 C. which contains, in solution, a heteroatom containing malonate. The treatment with TiCl4 is repeated and the solid is washed with hexane in order to eliminate any non-reacted TiCl4.
A further method comprises the reaction between magnesium alcoholates or chloroalcoholates (in particular chloroalcoholates prepared according to U.S. Pat. No. 4,220,554) and an excess of TiCl4 comprising the heteroatom containing malonate in solution at a temperature of about 80 to 120xc2x0 C.
According to a preferred method, the solid catalyst component can be prepared by reacting a titanium compound of formula Ti(OR)n-yXy, where n is the valence of titanium and y is a number between 1 and n, preferably TiCL4, with a magnesium chloride deriving from an adduct of formula MgCl2. pROH, where p is a number between 0.1 and 6 and R is a hydrocarbon radical having 1-18 carbon atoms. The adduct can be suitably prepared in spherical form by mixing alcohol and magnesium chloride in the presence of an inert hydrocarbon immiscible with the adduct, operating under stirring conditions at the melting temperature of the adduct (100-130xc2x0 C.). Then, the emulsion is quickly quenched, thereby causing the solidification of the adduct in form of spherical particles. Examples of spherical adducts prepared according to this procedure are described in U.S. Pat. No. 4,399,054 and U.S. Pat. No. 4,469,648. The so obtained adduct can be directly reacted with the Ti compound or it can be previously subjected to thermal controlled dealcoholation (80-130xc2x0 C.) so as to obtain an adduct in which the number of moles of alcohol is generally lower than 3 preferably between 0.1 and 2.5. The reaction with the Ti compound can be carried out by suspending the adduct (dealcoholated or as such) in cold TiCl4 (generally 0xc2x0 C.); the mixture is heated up to 80-130xc2x0 C. and kept at this temperature for 0.5-2 hours. The treatment with TiCl4 can be carried out one or more times. The heteroatom containing malonate can be added during the treatment with TiCl4. The treatment with the electron donor compound can be repeated one or more times.
The preparation of catalyst components in spherical form is described for example in European Patent Applications EP-A-395083, EP-A-553805, EP-A-553806, EP-A-601525 and WO98/44001.
The solid catalyst components obtained according to the above method show a surface area (by B.E.T. method) generally between 20 and 500 m2/g and preferably between 50 and 400 m2/g, and a total porosity (by B.E.T. method) higher than 0.2 cm3/g preferably between 0.2 and 0.6 cm3/g. The porosity (Hg method) due to pores with radius up to 10.000 xc3x85 generally ranges from 0.3 to 1.5 cm3/g, preferably from 0.45 to 1 cm3/g.
A further method to prepare the solid catalyst component of the invention comprises halogenating magnesium dihydrocarbyloxide compounds, such as magnesium dialkoxide or diaryloxide, with solution of TiCl4 in aromatic hydrocarbon (such as toluene, xylene etc.) at temperatures between 80 and 130xc2x0 C. The treatment with TiCl4 in aromatic hydrocarbon solution can be repeated one or more times, and the heteroatom containing malonate is added during one or more of these treatments.
In any of these preparation methods the desired heteroatom containing malonate can be added as such or, in an alternative way, it can be obtained in situ by using an appropriate precursor capable to be transformed in the desired electron donor compound by means, for example, of known chemical reactions such as esterification, transesterification etc. Generally the heteroatom containing malonate is used in molar ratio with respect to the MgCl2 of from 0.01 to 1 preferably from 0.05 to 0.5.
The solid catalyst component according to the present invention are converted into catalysts for the polymerization of olefins by reacting them with organoaluminum compounds according to known methods.
In particular, it is an object of the present invention a catalyst for the polymerization of olefins CH2xe2x95x90CHR, in which R is hydrogen or a hydrocarbyl radical with 1-12 carbon atoms, comprising the product of the reaction between:
(a) a solid catalyst component comprising a Mg, Ti and halogen as essential elements and an heteroatom containing ester of malonic acids;
(b) an alkylaluminum compound and, optionally,
(c) one or more electron-donor compounds (external donor).
The alkyl-Al compound (b) is preferably selected from the trialkyl aluminum compounds such as for example triethylaluminum, triisobutylaluminum, tri-n-butylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum. It is also possible to use mixtures of trialkylaluminum""s with alkylaluminum halides, alkylaluminum hydrides or alkylaluminum sesquichlorides such as AlEt2Cl and Al2Et3Cl3.
The external donor (c) can be of the same type or it can be different from the heteroatom containing malonate. Suitable external electron-donor compounds include silicon compounds, ethers, esters such as ethyl 4-ethoxybenzoate, amines, heterocyclic compounds and particularly 2,2,6,6-tetramethyl piperidine, ketones and the 1,3-diethers of the general formula (II): 
wherein RI, RII, RIII, RIV, RV and RVI equal or different to each other, are hydrogen or hydrocarbon radicals having from 1 to 18 carbon atoms, and RVII and RVIII, equal or different from each other, have the same meaning of RI-RVI except that they cannot be hydrogen; one or more of the RI-RVIII groups can be linked to form a cyclic group. Particularly preferred are the 1,3-diethers in which RVII and RVIII are selected from C1-C4 alkyl radicals.
Another class of preferred external donor compounds is that of silicon compounds of formula Ra5Rb6Si(OR7)c, where a and b are integer from 0 to 2, c is an integer from 1 to 3 and the sum (a+b+c) is 4; R5, R6, and R7, are alkyl, cycloalkyl or aryl radicals with 1-18 carbon atoms optionally containing heteroatoms. Particularly preferred are the silicon compounds in which a is 1, b is 1, c is 2, at least one of R5 and R6 is selected from branched alkyl, cycloalkyl or aryl groups with 3-10 carbon atoms optionally containing heteroatoms and R7 is a C1-C10 alkyl group, in particular methyl. Examples of such preferred silicon compounds are methylcyclohexyldimethoxysilane, diphenyldimethoxysilane, methyl-t-butyldimethoxysilane, dicyclopentyldimethoxysilane, 2-ethylpiperidinyl-2-t-butyldimethoxysilane and 1,1,1,trifluoropropyl-2-ethylpiperidinyl-dimethoxysilane. Moreover, are also preferred the silicon compounds in which a is 0, c is 3, R6 is a branched alkyl or cycloalkyl group, optionally containing heteroatoms, and R7 is methyl. Examples of such preferred silicon compounds are cyclohexyltrimethoxysilane, t-butyltrimethoxysilane and thexyltrimethoxysilane.
The electron donor compound (c) is used in such an amount to give a molar ratio between the organoaluminum compound and said electron donor compound (c) of from 0.1 to 500, preferably from 1 to 300 and more preferably from 3 to 100. As previously indicated, when used in the (co)polymerization of olefins, and in particular of propylene, the catalysts of the invention allow to obtain, with high yields, polymers having a high isotactic index (expressed by hitch xylene insolubility X.I.), thus showing an excellent balance of properties. This is particularly surprising in view of the fact that, as it can be seen from the comparative examples here below reported, the use as internal electron donors of malonate compounds not containing heteroatoms gives worse results in term of yields and/or xylene insolubility.
Therefore, it constitutes a further object of the present invention a process for the (co)polymerization of olefins CH2xe2x95x90CHR, in which R is hydrogen or a hydrocarbyl radical with 1-12 carbon atoms, carried out in the presence of a catalyst comprising the product of the reaction between:
(a) a solid catalyst component comprising a Mg, Ti, halogen and a heteroatom containing malonate;
(b) an alkylaluminum compound and, optionally,
(c) one or more electron-donor compounds (external donor).
Said polymerization process can be carried out according to known techniques for example slurry polymerization using as diluent an inert hydrocarbon solvent, or bulk polymerization using the liquid monomer (for example propylene) as a reaction medium. Moreover, it is possible to carry out the polymerization process in the gas-phase operating in one or more fluidized or mechanically agitated bed reactors.
The polymerization is generally carried out at temperature of from 20 to 120xc2x0 C., preferably of from 40 to 80xc2x0 C. When the polymerization is carried out in the gas-phase the operating pressure is generally between 0.5 and 10 MPa, preferably between 1 and 5 MPa. In the bulk polymerization the operating pressure is generally between 1 and 6 MPa preferably between 1.5 and 4 MPa. Hydrogen or other compounds capable to act as chain transfer agents can be used to control the molecular weight of polymer.
The following examples are given in order to better illustrate the invention without limiting it.
Characterizations
The malonates used in the present invention were prepared by Knoevenagel condensation of halogenated ketones with diethyl malonate, see Tetrahedron, 29, 635, (1973), followed by selective reduction of the double bond, (J. March in xe2x80x9cAdvanced Organic Chemistryxe2x80x9d IV Ed. (1992) pp. 771-781). The malonates having the alcoholic moiety different from ethyl were prepared by transesterification of the corresponding diethyl malonate as described in Example 1 of DE 2822472.
Propylene General Polymerization Procedure
In a 4-liter autoclave, purged with nitrogen flow at 70xc2x0 C. for one hour, 75 ml of anhydrous hexane containing 800 mg of AlEt3, 79.8 mg of dicyclopentyldimethoxysilane and 10 mg of solid catalyst component were introduced in propylene flow at 30xc2x0 C. The autoclave was closed. 1.5 Nl of hydrogen were added and then, under stirring, 1.2 Kg of liquid propylene were fed. The temperature was raised to 70xc2x0 C. in five minutes and the polymerization was carried out at this temperature for two hours. The non-reacted propylene was removed, the polymer was recovered and dried at 70xc2x0 C. under vacuum for three hours and, then, weighed and fractionated with o-xylene to determine the amount of the xylene insoluble (X.I.) fraction at 25xc2x0 C.
Determination of X.I.
2.5 g of polymer were dissolved in 250 ml of o-xylene under stirring at 135xc2x0 C. for 30 minutes, then the solution was cooled to 25xc2x0 C. and after 30 minutes the insoluble polymer was filtered. The resulting solution was evaporated in nitrogen flow and the residue was dried and weighed to determine the percentage of soluble polymer and then, by difference the Xylene-Insoluble fraction (%).